Human Body a Visual Encyclopedia

Each spot is a colony of
thousands of bacteria that
grew from a single bacterium
in the dirty handprint.

SURGERY DISEASE DEFENSES

WOW! If disease or injury damages an organ
inside the body, doctors may need to
Given warmth and perform surgery to repair the damage.
sufficient food, a single Patients are first given drugs called
bacterium can divide and anesthetics to make them fall asleep
and to prevent pain. The surgeon then
give rise to 5 billion makes precise cuts in the skin in order
trillion offspring in to open up the body and gain access to
the damaged area. Surgeons work in
just one day. spotlessly clean operating theaters to
prevent germs from entering the
patient’s body during an operation.

FIGHTING CANCER

Sometimes body cells stop
working properly and begin to

multiply out of control like
germs, forming lumps known as

tumors. This deadly disease is
called cancer. Cancer is difficult
to treat because drugs that attack

cancer cells also harm healthy
body cells. To help destroy

tumors, doctors fire beams of
powerful radiation at them—a
treatment called radiotherapy.

▶ RADIOTHERAPY This patient
is being treated for skin cancer. A
beam of radiation is pointed at a

tumor from several different angles,
killing the cancer cells without

harming the healthy tissue around it.

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DISEASE DEFENSES Spare parts ▲ GLASS EYES Artificial eyes
look realistic but they do not
In the past, losing an important part of the restore vision. However, scientists
body due to disease or injury led to death or are developing implants that
severe disability. Today, doctors can repair many could restore some form of vision
parts of the body with artificial replacements. to people who are blind.
In years to come, they may be able to replace
organs with fresh new ones grown in a lab from
your own body cells. This technology would
allow us to live decades longer than today.

REBUILDING THE BODY

Some of the artificial parts that doctors use to
repair damaged bodies are mechanical or electrical
devices made of metals and plastics. Others, such
as artificial skin or transplanted organs, are made
of living tissue. Most of these spare parts do not
work as well as the organs they replace.

▶ NEW SKIN Scientists ▼ HIP JOINT Damaged by
have discovered how to age or disease, some joints, such
grow sheets of artificial as the hip, can be repaired
skin from a person’s skin with an artificial replacement.

cells. Although they’re very
thin, these sheets may soon

be used to repair damage
caused by severe burns.

STEM CELLS

Some of the cells in the human body
have an amazing ability: They can
multiply and develop into any kind of
tissue, such as skin, blood, or nerves.
Such cells are known as stem cells.
Scientists are trying to harness this
ability of stem cells and create new
tissues or organs to repair or replace
body parts that are injured or diseased.

100

BLADE RUNNER DISEASE DEFENSES

South African athlete Oscar Pistorius lost the lower part of
both his legs when he was a baby. He now walks and runs on
J-shaped artificial feet made of carbon fiber. These are so good
that Pistorius, nicknamed “Blade Runner” by his fans, is able
to compete against able-bodied athletes, as in the 2011 World
Athletics Championships, shown below.

▲ EAR IMPLANT A cochlear
implant picks up sound and
transmits it to the inner ear,
giving some sense of hearing
to people who are deaf.

PACEMAKER ▲ A computer ORGAN TRANSPLANTS
Implanted into the chest controls the motors
wall, a pacemaker sends an that make the arm The most common way of replacing
electric signal along a wire and hand move. a damaged internal organ is to use a
to the heart, controlling healthy organ from a donor—an
the rate at which it beats. ◀ ROBOTIC ARM organ transplant. Transplants can
This high-tech mechanical save lives and make people healthy
arm is controlled by thought again, but recipients must take
alone. Sensors on the shoulder powerful drugs to stop their bodies
pick up nerve signals inside from rejecting the new organs.
the wearer’s body and relay
them to a computer, which
controls the arm’s movements.

A motor inside the
elbow makes the
arm bend.

◀ NEW BLADDER The
bladder is one of the few
organs that scientists can
grow in a lab, using a
patient’s own body cells.

▲ KIDNEY TRANSPLANT Surgeons
prepare a donated kidney before implanting
it into a recipient.

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DISEASE DEFENSES Ancient remedies WOW!

Before the age of science, people used all sorts of weird and People used to think
wacky remedies to try and cure diseases. Many people visited diseases were spread by
witch doctors or priests in search of magical cures. Others foul smells. Powerful
made their own medicines, following traditional old wives’ perfumes were used to
recipes. Many of the ancient remedies were useless or even
dangerous, but a few really did work and are still used today. ward off illness.

HERBAL MEDICINE

Plants have been used as medicines all
over the world for thousands of years
and they are still popular today. Some
of our modern drugs were discovered
thanks to ancient herbal remedies.
The painkiller aspirin, for instance,
comes from the bark of willow
trees, which people once used
to make a pain-relieving tea.

▶ BROKEN ARM
This engraving from the
1500s shows how a man’s
broken arm was treated.
Turning the screw pulled
the arm straight, moving
the broken bones back
into position.

102

CUPPING A HOLE IN DISEASE DEFENSES
THE HEAD
The ancient practice of
cupping was once widely Stone age people believed
believed to help cure diseases that diseases were caused
by encouraging blood flow. by evil spirits. The cure,
Small cups are heated and they thought, was to drill
placed on the skin. As the air a hole in the skull to
inside a cup cools, it contracts, release the spirit—
sucking up an area of skin and a technique called
drawing blood to the surface. trepanning. Some
Red rings and sometimes prehistoric skulls found by
bruises are left afterward. archaeologists have as many
as 40 holes drilled in them.
BARBER SURGEONS
BLOODLETTING
In medieval Europe, all operations from tooth
extraction to mending broken arms were performed Removing blood, or
by barbers. Surgery was often deadly since barbers bloodletting, was a
had little idea how to stop wounds from getting very common medical
infected. And patients had to stay practice for centuries. It
awake during treatment since was thought to put body
general anesthetics fluids back into balance.
didn’t exist. Blood was drawn by
cutting the skin, by
▲ BLOODSUCKERS piercing veins and
The Roman Emperor Galerius arteries, or by using
was treated with leeches to bloodsucking leeches.
cure an “abominable stench.”

MUD BATHS

Bathing in pools of mud, hot springs, or
mineral water has long been a popular
treatment for joint pain (arthritis), skin
complaints, and other conditions. Even
today, people travel great distances to visit
famous spa towns and “take the waters.”

103

LUNGS AND BREATHING LUNGS AND
BREATHING

The cells in your body can’t LUNGS AND BREATHING
survive without a continual
supply of oxygen from the
air. Your lungs take in air
with every breath, bringing
oxygen to your blood to be
carried around the body.

Airways Air is warmed
and cleaned as it
We never really think about breathing because it passes through the
nasal cavity.

is such an automatic process, but it is vital to our

LUNGS AND BREATHING survival. Every inward breath brings a new supply The epiglottis
of air into the network of tubes that make up the is a flap at the
respiratory system. These take air deep into the lungs, front of the
voice box.

where the gas oxygen, which is vital for life, passes

into the blood to be carried all around the body. The voice
box, or larynx,
produces sounds.

THE RESPIRATORY SYSTEM

Your lungs and the airways that carry air in and
out of your body are located in your head and
chest. The airways include the nasal cavity, the
throat, the larynx (voice box), and the branching
passages inside your lungs. Incoming air is
cleaned as it travels through your nose and
trachea to remove dirt and germs that could
block or damage the delicate lungs.

Oxygen ▶ THIS WAY
TO THE LUNGS
The ridged appearance of
the trachea is produced by rings
of rubbery cartilage that
hold it open during breathing
and stop it from closing up.

OXYGEN SUPPLY

We breathe in oxygen and
breathe out waste carbon
dioxide. So why doesn’t our
oxygen supply run out? Plants
ensure there is a steady supply
in the air by releasing oxygen
during photosynthesis, the
process that uses sunlight and
carbon dioxide to make food.

Carbon dioxide

106

NO CHOKING

Every time you swallow food or drink, your breathing
stops. A flap of tissue called the epiglottis drops over
the entrance to your voice box to stop food from
getting into the airway to your lungs and making you
choke. If this happens, however, coughing forces food
out of the airway and back into your throat.

Breathing LUNGS AND BREATHING

▲ AIR CLEANERS The epiglottis Inhaled air
The trachea is lined with sticky is upright. Esophagus
mucus that traps dirt and germs Air flows
in the incoming air. Tiny cilia toward the lungs.
(green) move the dirty mucus to
the throat, where it is swallowed. Swallowing

Air is carried to Food is pushed
and from the lungs into the
by the trachea. esophagus.

Curved ribs form The epiglottis folds
a protective cage over to cover the
around the lungs. entrance to
the voice box.
The airways
become more finely
branched as they
penetrate deeper
into the lung.

The heart pumps WOW!
blood to the lungs
to pick up oxygen. Every day, you
swallow about a
Protective glassful of slimy
membranes mucus produced by
cover the lungs.
your airways.

A sheet of muscle called
the diaphragm helps
inflate the lungs.

107

In and out AIR IN

Your body cells need constant supplies of oxygen. Air is drawn into the body by the
They also need to get rid of waste carbon dioxide movement of the rib muscles and
gas. This exchange of gases happens in your lungs. the diaphragm—a sheet of muscles
Breathing in and out ensures that fresh under the lungs. When you breathe
supplies of oxygen are brought in, the diaphragm tightens and pulls
in and stale air containing down. At the same time, your rib
carbon dioxide is removed. muscles tighten and pull your
The lungs cannot move by ribcage upward and outward.
themselves, so the process
relies on muscles in the chest As a result, your chest gets
to suck air in and push it out. larger and your lungs suck
LUNGS AND BREATHING in air through your
mouth and nose.
You take in about 40,000 breaths of air every day.
Oxygen (20.8%)

Nitrogen Nitrogen and water
vapor (79.16%)

Carbon dioxide
(0.04%)

Oxygen The ribcage moves
upward and
Other outward as the rib
gases muscles contract.

WHAT IS AIR? The lungs
get bigger
Air is a mixture of gases and suck
that surrounds our planet. in air.
As you can see from this
balloon diagram, air is The
mostly nitrogen (about diaphragm
78 percent) and oxygen flattens
(about 21 percent), plus and pulls
small amounts of other downward.
gases. Oxygen is the only
part of the gas mixture
that your body uses.

108

AIR OUT CONTROL CENTER LUNGS AND BREATHING

When you breathe out, your diaphragm relaxes You don’t have to think about breathing. The brain stem
and springs back into its natural, curved shape, pushing (orange) at the base of your brain (green) automatically
up against your lungs. At the same time, your rib muscles controls your breathing rate. This control center monitors the
relax and let your ribcage drop back downward and amount of carbon dioxide in your blood. If the carbon dioxide
inward. As a result, your lungs are squeezed and air is level rises, during exercise for example, your breathing rate
pushed out through your mouth and nose. The air you goes up to supply more oxygen to your muscles and to flush
breathe out contains less oxygen and more carbon out the excess carbon dioxide.
dioxide than the air you breathed in.

The brain stem
controls the body’s
breathing rate.

80.4% Nitrogen
and water vapor

15.6%
Oxygen

4% Carbon
dioxide

The ribcage moves
downward and inward
as the rib muscles relax.

The lungs FAST OR SLOW?
are squeezed,
pushing out air. At rest, we breathe in and out
between 12 and 15 times a
This is minute. During exercise, such
the size as running, our breathing rate
of the chest can more than double and we
when air is breathe more deeply. This is
breathed in. because our muscles are working
harder and need more oxygen to
The release the energy required for
diaphragm movement. They also produce
relaxes and more carbon dioxide, which
pushes must be removed.
upward.
109

LUNGS AND BREATHING

LUNGS AND BREATHING

BREATHING UNDERWATER

A continual supply of oxygen from
the air is vital for the human body.
Without it, brain cells start dying
in large numbers after only five
minutes. Scuba divers breathe air
underwater from a compressed-air
tank carried on the back. One tank
has enough air to last 45 minutes.

Inside the lungs The trachea
carries air to and
Packed into your chest are a pair of soft, spongy lungs. from the lungs.
Their job is to get oxygen into, and carbon dioxide
LUNGS AND BREATHING out of, your blood. This transfer is made possible
by millions of tiny air bags inside the lungs that
are supplied by a rich network of blood vessels.

Blood is carried
into the lung by the
pulmonary artery.

Blood is carried out
of the lung by the
pulmonary vein.

LUNG STRUCTURE

Air is carried to the lungs by a tube
called the trachea. This branches
into two tubes called bronchi, which
branch further into smaller and smaller
tubes called bronchioles. At the end of
the tiniest bronchioles are 150 million
little air bags, called alveoli, which
swap oxygen for carbon dioxide.

Blood vessel

Air bag The right bronchus
(alveolus) carries air to and
from the right lung.
▲ AIR BAGS The bronchioles end in tiny,
lumpy air bags called alveoli. Oxygen from Bronchioles
the air inside alveoli passes into the blood
capillaries that surround them.

112

The left bronchus BRONCHIAL TREE
carries air to and
from the left lung. The branching network of
airways inside the lungs is
sometimes called the bronchial LUNGS AND BREATHING
tree. As you can see here, it
looks like an upside-down
tree with the trachea as
the trunk, bronchi as the
branches, and the tiny
bronchioles as twigs.

The left lung
opened up to
show its structure.

LOOK CLOSER: DUST GOBBLERS

When you breathe in air, most dust particles, pollen
grains, and germs are trapped by sticky mucus in the
nose and airways. But some of them travel deep into
the lungs. Before they can do any harm, they are
gobbled up by wandering macrophages.

▲ GERM EATER A macrophage is a type of white
blood cell. It moves by extending its narrow “arms,”
which it also uses to grab foreign particles.

INTO THE BLOOD Oxygen passes
into the blood.
This is a close-up view of what
happens at the junction between Blood cell
an alveolus and a capillary.
The heart Oxygen travels from the
fits into alveolus into the
this space. blood, and carbon
dioxide moves in
the opposite
direction.

Slippery membranes Inside of alveolus
surround the lungs.

Carbon dioxide passes out of
the blood into the alveolus.

113

Coughs and sneezes

Your lungs and airways are always at work, taking in fresh air

and pushing out stale air, and most of the time you don’t

LUNGS AND BREATHING notice them doing it. Occasionally, however, they might WOW!
surprise you with an unexpected cough, sneeze, yawn,
or hiccup. These processes mostly play a vital role in

keeping you healthy, but some are a bit of a mystery. You can’t cough, sneeze,

yawn, hiccup, or laugh

when you’re dreaming,

since most of your

SNEEZING muscles are paralyzed
during dreams.
If something itchy gets in your nose, your body

clears it out with a deafening blast of air: a sneeze.

After a sharp intake of breath, your eyes close and

your rib muscles tighten to squeeze your lungs and blast

air out, often with a brief scream. Your tongue rises to

direct air into your nose, but most of the blast often

comes out of the mouth. germs out

Sneezes clear o

f your nose ut spread them to other people.b

HICCUPS

Hiccups happen when your diaphragm muscle twitches. The sudden movement
of the diaphragm causes a very sharp intake of breath, and the rush of air makes
the vocal cords at the top of the trachea snap shut, blocking the air and
producing a “hic” sound. Hiccups have no known purpose and can start for no
apparent reason. They usually stop after a minute or two, but in rare cases they
last longer. One man had a bout of hiccups that lasted 68 years.

“Hic” “Up” LUNGS AND BREATHING

Air rushes in. Air leaves. YAWNING

The vocal The vocal cords No one knows what purpose yawning
cords snap shut, open again. serves. Yawns aren’t an efficient way of
blocking the air. breathing, and although we yawn when
The diaphragm we’re tired, we also do it when we’re
The diaphragm relaxes and nervous. To add to the mystery, yawns
twitches and pulls moves up, are contagious—if you see someone
flat, pulling air pushing air out. yawn, you’ll probably do it too.
into the lungs.

LAUGHING SNORING COUGHING

When we laugh, the vocal cords at the The roof of your mouth is hard at the Coughing gets rid of specks of dirt
top of the trachea open and close front but soft at the back, where it or germs that have gotten into your
repeatedly, chopping our breaths into forms a flap of tissue separating your airways. First you take a deep breath.
segments and making a “ha, ha, ha” or mouth and nose. In some people, this Then your lungs squeeze, but the
“ho, ho, ho” sound. Laughter triggers flap wobbles around during sleep, vocal cords stay shut to build up
the release of brain chemicals called making a loud noise—snoring. People pressure. When they open, air shoots
endorphins, which make us feel great. snore less if they lie on one side. out in a sudden blast.

115

LUNGS AND BREATHING Making sounds

Many animals make sounds, but humans are the only animals
that can communicate using spoken words. Both speech and
language are controlled by your brain. It sends out instructions
that make your respiratory (breathing) system produce
sounds that can be understood by those around you.

WHAT IS SOUND? WOW!

Throw a pebble into a pond and circular Men have deeper
ripples will move outward from the point voices than women
of impact. In the same way, if you pluck because their vocal cords
are longer and vibrate
a guitar string so it vibrates, sound
waves will move outward through more slowly.
the air. These sound waves are
picked up by your ears.

VOICE BOX

The vocal cords in your voice box (larynx) make the sounds that are shaped
into speech. These cords are separated when you are silent and breathing
normally. When you speak, your brain sends signals to the voice box muscles
to pull the vocal cords together and make them tight. When air pushes
between these muscles, they vibrate and create sounds.

▲ VOCAL CORDS Sounds are The vocal ▲ VOCAL CORDS
TAUT Bursts of air produced by cords stretch OPEN During normal
passing between the the voice box across the breathing, the open
taut vocal cords make (larynx). larynx. vocal cords allow air
them vibrate and to move to and from
produce sounds. The trachea the lungs.
carries air
to and from The esophagus
the lungs. is a part of the
digestive system.

116

SHAPING SPEECH FAST FACTS

Under orders from your brain, the ■ Around 6,900 languages are spoken in
muscles controlling your tongue, lips, the world today. The top five most spoken
and cheeks shape the sounds coming languages are Mandarin Chinese,
from your vocal cords. They create English, Spanish, Hindi, and Russian.
a sequence of words, spoken in a ■ The vocal cords of a soprano—a
recognizable language, which reveals woman with a high singing voice—
your thoughts and feelings to others. vibrate at up to 2,000 times a second.
■ The vocal cords of a bass—a man
Tongue muscles with a low singing voice—vibrate LUNGS AND BREATHING
help shape sounds. just 60 times a second.

IN CONTROL

These two scans show which areas of your brain are used
when you speak (left) and when you listen to spoken words
(right). In the first scan, Wernicke’s area finds the correct
words to match what the brain has to say and sends signals
to Broca’s area. This, in turn, sends signals to the voice box
and the mouth instructing them to produce speech.

Broca’s area Speaking Wernicke’s area Listening The hearing
controls speech. “understands” words. area of the
brain
MAKING MUSIC
▶ HEARING Sound
Some people can use their breathing systems to make sounds waves from the speaker’s
much louder than their own voices. Controlled bursts of air from mouth enter the listener’s
this musician’s lungs create buzzing vibrations in her lips. These ears. Here they are detected
sound vibrations enter and travel through the long tube-shaped by sound receptors that
trumpet, which makes the sounds much louder. send signals to the brain.

117

FUELING THE BODY FUELING
THE BODY

Just like a car, your body FUELING THE BODY
needs a supply of fuel to keep
you going. All your energy
comes from food, which your
digestive organs break down
into simple molecules for
your body to absorb.

Food for life

FUELING THE BODY You need to eat food so that your body can get the nutrients it needs to Peppers supply minerals
grow, and to repair and maintain itself. Some nutrients are needed in and vitamins and are a
large amounts. These include carbohydrates, which supply energy, and good source of fiber. This
proteins, which are used to build and repair your body’s cells. Vitamins helps speed up digestion.
and minerals are needed in smaller quantities.

WOW! A HEALTHY DIET

Water is an important The nutrients you need to stay healthy
part of your diet. Some can be found in food. Different types
of food provide different nutrients.
fruit contains a lot This platter shows how much
of liquid—apples are you should eat of each type,
compared to the others.
84 percent water. For example, you should
eat a lot of fresh fruits
and vegetables, but not
very much meat or fat.

Carrots contain vitamin A.
You need this vitamin to
keep the eyes healthy.

BREAKING DOWN FOOD

The nutrients that we need are often “locked” inside food and can’t be
used by your body right away. Your digestive system breaks down
complicated foods into simple sugars, fatty acids, and amino acids—the
basic building blocks of protein—that the body can absorb and use.

Fatty acid ◀ FATS These are broken
down into simpler glycerol
and fatty acid molecules.

Fat Glycerol

◀ PROTEINS These are
broken down into separate
amino acids.

Amino acids

Protein Sugars ◀ CARBOHYDRATES Whole grains are a
Complex carbohydrates, such good source of some
Carbohydrate as starch, are converted into B vitamins. These help
120 simple sugars, such as glucose. keep your cells healthy.

▶ RICKETS This X-ray shows the VITAMINS AND MINERALS
bent leg bones of a child with rickets.
Rickets occurs when the body doesn’t Although they are only needed in
get enough vitamin D. This vitamin tiny amounts, vitamins and minerals
are essential for good health. A healthy
is essential for normal bone growth. diet should include vitamins A,
It is found in fish and eggs. Your B group, C, D, and E. Important
body can also produce it when minerals include calcium, for healthy
you get sunlight on your skin. teeth and bones, and iron, which is
needed to make red blood cells.
Citrus fruits, such as
lemons, are a good source FUELING THE BODY
of vitamin C, which can
help you fight infections.

Beans and nuts are a
good source of protein,
essential for cell growth
and repair.

Fish, meat, and LIND’S LIMES
eggs are high in
protein.

Sweets and Sailors used to develop a deadly disease
fats should be called scurvy on long sea voyages. In 1747,
eaten in small a navy doctor named James Lind found
amounts. that feeding them citrus fruits, such as
limes, cured them. Later, scurvy was
shown to result from a lack of vitamin C.

FEELING HUNGRY The area of your
brain that controls
Hunger and fullness are your appetite.

sensations produced by a

part of your brain called the

hypothalamus. Before a

meal, the stomach releases

a hormone that makes

you feel hungry. After a

meal, fat tissue releases

another hormone

that makes you

feel full.

Cheese and other dairy
products are a good
source of calcium,
needed for healthy bones.

Bread and other
starchy foods are
the body’s main
source of energy.

Digestion Food is moved between
the teeth and toward the
FUELING THE BODY Food provides the body with nutrients. The teeth back of the mouth for
But releasing those nutrients from food cut and swallowing by the tongue.
requires a process called digestion. First, crush food into
the food has to be cut up and churned small pieces. The throat (pharynx)
into small particles. This makes it connects the mouth
easier for enzymes to work on the Salivary glands to the esophagus.
complex chemicals that make release saliva into
up food and split them into the mouth. The epiglottis stops
substances that can be used by food from going down
the body. All of this happens The esophagus the trachea during
inside the digestive system. transports food swallowing.
from the throat
to the stomach. The trachea, part of
the respiratory
system, carries air
to the lungs.

The stomach
stores and partially
digests food.

DIGESTIVE SYSTEM Nutrients are
processed by
The digestive system consists of the liver.
a long, muscular tube called the
digestive tract, which runs from Fats are turned into tiny
the mouth to the anus. It has droplets by bile, a green
several distinct regions, including fluid released by the
the esophagus, stomach, small gall bladder.
intestine, and large intestine—
each with its own tasks. Other The pancreas releases
organs that help digestion, digestive enzymes into
such as the gall bladder and the small intestine.
pancreas, add digestive
chemicals at various points Most food is digested in
along the way. the small intestine. The
nutrients that are released
WOW! are absorbed into the
bloodstream.
During an average
lifetime, a person will In the large intestine,
eat their way through, water is absorbed
from waste to form
and digest, at least feces (poo).
20 tons of food.
The rectum holds
and expels feces.

The anus is the
opening at the end
of the digestive tract.

122

ENZYMES IN ACTION

Enzymes are proteins that speed Long food Long food
up the breakdown of complex molecule molecule
molecules into much simpler splits
nutrients that can pass into the
bloodstream to be used by cells. Short,
Without enzymes, digestion simple
nutrient
molecules

would be so slow that we would Enzyme Active site Enzyme ready
of enzyme for action
starve. Each enzyme acts on a FUELING THE BODY

specific food type, such as the ▲ ATTACHMENT Inside the ▲ SPLITTING MOLECULES ▲ NONSTOP ACTIVITY
enzyme pepsin in stomach juice digestive tract, a food molecule The active site breaks some of The enzyme releases the molecule
that breaks down proteins into attaches itself to a region of its the chemical bonds in the food once it has split apart. One
molecule, splitting it into smaller enzyme can process hundreds
simpler nutrients. You can see specific enzyme called the nutrient molecules. of molecules a second.

here how an enzyme works. active site.

TAKING TIME 00:00:10 LOOK CLOSER: FOOD POISONING

It only takes a few seconds for food chewed Ten seconds Most bacteria and other microorganisms in food
in the mouth to arrive in the stomach. But, after swallowing, are destroyed by the harsh, acidic conditions
as you can see from this stretched-out view food arrives in found in the stomach. But some harmful bacteria
of the digestive tract, the rest of the the stomach. survive and they, or their poisons (toxins), irritate
process takes up to two days longer. the stomach and intestines, giving you food
This ensures that food is properly 03:00:00 poisoning. This causes symptoms such as
digested to release as many nutrients vomiting (throwing up) and diarrhea (runny poo).
as possible, and that Food in creamy,
these nutrients are liquid form is
all absorbed into squirted into the
the bloodstream. small intestine.

06:00:00

Food is now almost
completely digested
and its nutrients
are being absorbed.

20:00:00 08:00:00 ▲ STOMACH BUG This micrograph shows
Salmonella, a bacterium that causes food
Water is absorbed Watery, indigestible poisoning. The bacterium is rod-shaped and
as waste passes along waste leaves the can move by wiggling its hairlike flagella to
the large intestine. small intestine. push itself forward.

Semi-solid feces 32:00:00 123
form as water
is removed. Feces arrive
in the rectum
20 to 44 hours
after eating.

What a mouthful!

FUELING THE BODY If you tried to swallow a large piece of food The parotid gland
without chewing it, you would probably releases saliva
choke. You must first grind it up by into the mouth.
repeatedly bringing your teeth together
to chop and crush it into smaller pieces. Esophagus
While you chew, the food is moistened Trachea
with saliva, and moved and mixed
up by your tongue. In addition to
making food moist, saliva contains
an enzyme that starts to digest it.

DOWN THE HATCH The roof of the
mouth is called
The first part of the digestive the hard palate.
system, the mouth, contains the
teeth and tongue. Slippery saliva A duct from the
rushes into the mouth from three parotid gland carries
pairs of salivary glands situated saliva to the mouth.
under the tongue and in front
of the ears. Saliva lubricates the The incisor teeth
food as it is chewed into a pulp. cut up food as it
A ball of food is then pushed enters the mouth.
into the throat and travels down
the esophagus to the stomach. The tongue moves Two pairs of glands
food between the release saliva under
teeth, and tastes it. the tongue.

Canine

Molars OPEN WIDE
Premolars
Adults have a full set of 32
teeth, which vary in shape
and size according to what
they do. Chisel-like
incisors cut and slice food,
while pointed canines grip
and pierce. Farther back
are the premolars and
molars, which chew and
grind food between the
pointed tips of their crowns.

Incisors

124

WOW! INSIDE A TOOTH ▲ ENAMEL is the hardest FUELING THE BODY
material in the body and
Your six salivary A tooth has two layers: a smooth enamel crown forms the crown of the tooth.
glands release nearly that provides a hard biting surface, and the It consists of microscopic rods
two pints (one liter) dentine beneath, which also forms the root. of calcium phosphate.
of watery, slimy saliva Inside the dentine is the pulp cavity containing
blood vessels that supply tooth cells, and The root of the tooth
into your mouth nerve endings that detect pressure, heat, is embedded in a
every day. and cold, and also signal pain. socket in the jawbone.

Crown A band of tough
tissue called a
▼ DENTINE is harder The gum forms a ligament anchors the
than bone and forms the collar around the tooth in its socket.
framework of the tooth. base of the crown.
Its honeycomb structure Jawbone
helps it resist the enormous Pulp is the soft
squashing forces that are tissue containing Blood vessels
created during biting. nerve endings supply the tooth
and blood vessels. with nutrients.

A nerve provides the
tooth with feeling.

FROM MOUTH TO STOMACH

Swallowing, the process that moves food from the to push food into your throat. The other two stages,
mouth to the stomach, has three phases. The first, in in the throat and esophagus, are reflex actions that
the mouth, is under your control, so you decide when happen automatically.

Soft Contracted
palate muscle

Food Food
bolus bolus

▲ MOUTH As chewing Relaxed Movement
reaches completion, the muscular muscle towards
tongue molds food particles into Epiglottis stomach
a bolus (ball) that is pushed into
the throat. Esophagus

▲ THROAT Muscle ▲ ESOPHAGUS Rippling
contractions push the bolus waves of muscle contractions
towards the esophagus, while the in the esophagus wall push
soft palate and epiglottis stop it the bolus to the stomach.
from entering the trachea. This takes about ten seconds.

125

FUELING THE BODY In the stomach Within this area is the
cardiac sphincter. It stops
The stomach is a muscular “bag” that sits just below the food from flowing back
diaphragm muscle in the middle of the chest. It has two up into the esophagus.
key roles. When you eat, it releases an acidic gastric
juice that starts to break down the proteins in ◀ PYLORIC
food. It also stores food, releasing it at a SPHINCTER
steady rate so that the small intestine A sphincter is a ring of
has time to digest it efficiently. strong muscle. The pyloric
sphincter, seen here through
FILLING AND EMPTYING an internal camera, remains
tightly closed as the stomach
The process of filling and emptying the stomach depends on the processes food.
type of food eaten, but it takes at least three hours. During this
time, food is partially digested and made ready for the main part Folds in the
of digestion in the small intestine. Only when the meal has been muscular walls
turned into liquid form is it released into the duodenum. disappear as the
stomach expands.

Food is mixed ◀ DURING A MEAL
with gastric As the stomach fills
juice. and expands, recently
chewed food is mixed
with gastric juice by
contractions of the
stomach’s wall.

◀ 12 HOURS

The wall of the AFTER EATING
stomach contracts. Food is partly digested

by gastric juice and

churned by powerful

muscular contractions

into a creamy liquid

The pyloric called chyme.
sphincter keeps

food in the SQUEEZE AND CHURN
stomach.
The stomach wall has three layers
The pyloric ◀ 34 HOURS of muscles, arranged at different
sphincter AFTER EATING The angles to each other. These produce
opens. pyloric sphincter opens powerful contractions that squeeze
the food and mix it with gastric
slightly and the stomach juice. An enzyme called pepsin gets Chyme
to work on food proteins, breaking (liquid food)
wall contracts to push them down into simpler substances.

small quantities of chyme

into the duodenum,

Chyme is squirted which is the first part
into the duodenum. of the small intestine.

126

Your stomach can stretch to more t FUELING THE BODY

han 20 times its size after eating.
A JUICY TALE

In 1822, fur trapper Alexis St. Martin accidentally
shot himself in his side. This left a permanent
opening to his stomach called a fistula. American
army surgeon William Beaumont, who treated St.
Martin, realized he could use his patient to find out
how digestion in the stomach worked. Beaumont
placed different types of food through the opening to
see how fast they were digested. He also, as shown
here, extracted gastric juice to investigate its
composition and action on food.

The longitudinal WHAT MAKES YOU SICK?
muscle layer
extends the Vomiting, or throwing up, happens when
length of the something irritates the lining of the stomach.
stomach. This triggers the vomiting reflex. The
diaphragm and abdominal muscles contract,
The circular muscle squeezing the stomach so that food is forced
layer wraps around up the esophagus and out of the mouth.
the stomach.
Vomiting center in
The oblique muscle the brain triggers
layer runs diagonally vomit reflex
around stomach.
Soft palate
blocks entrance
to nasal cavity

Epiglottis
blocks entrance
to trachea

▶ STOMACH Gastric pit Diaphragm
LINING pushed
This magnified view downward
of the stomach’s lining
shows the openings of the Pyloric
glands that release digestive sphincter
gastric juice into the stomach. closes

Abdominal
muscles push
inward

127

FUELING THE BODY Gut The pancreas
Liver produces enzymes
and hormones.
reactions
The gall bladder
At nearly 23 ft (7 m) in length, the stores and
small intestine is the longest and most releases bile.
important part of the digestive system.
With the help of the pancreas and gall The large intestine lies in
bladder, the small intestine completes front of the duodenum,
the digestive process. It then absorbs the first part of the
all the released nutrients so that they small intestine.
can be used by your body’s cells.

LONG AND WINDING JOURNEY The second part
of the small
This long, middle part of the digestive tract intestine is
is coiled up to fit into the abdomen. The called the
small intestine has three sections. The short jejunum.
duodenum receives chyme from the stomach
and digestive juices from the gall bladder and
pancreas. The longer jejunum and ileum are
where most digestion and absorption
of food takes place.

GALL BLADDER AND PANCREAS

The gall bladder and pancreas Bile duct Appendix
release fluids through a common
duct into the duodenum. This Pancreatic The ileum is the
kick-starts digestion in the small Pancreas duct final and longest
intestine. The baglike gall bladder part of the small
stores bile made by the liver. Bile intestine.
turns fats into tiny droplets that
are much easier to digest. The Gall bladder
pancreas makes pancreatic juice.
This contains enzymes that break
down carbohydrates, proteins,
and fats in the food we eat.

Opening of Duodenum
pancreatic
and bile ducts

128

Muscular
wall

◀ INSIDE VIEW This cross-section FUELING THE BODY
of the small intestine reveals
its structure. Muscles in its wall
create wavelike contractions
that both mix food and move it
onward. The lining is covered
with tiny, fingerlike bumps
called villi.

WOW! ▶ VILLI These are
some of the millions
The small intestine of microscopic villi lining
is coiled inside the the small intestine. Villi provide a huge
abdomen, but stretched surface area for digestion and absorption
out it would be as long to take place. If stretched out, the villi in
as four adults laid your small intestine would cover an area
roughly the size of a tennis court.
head to toe.

Villi Capillary network Food molecule

inside a villus in a capillary

DIGEST AND ABSORB

Inside the small intestine,
enzymes attached to the surface
of villi complete the process of
digestion. They break down food
into simple nutrients—glucose,
amino acids, and fatty acids.

▲ IN THE MIDDLE The ▶ ABSORPTION Glucose and
small intestine, which winds amino acids are absorbed into the
its way from the stomach to the capillary networks inside villi and
large intestine, takes up much are carried in the blood to the liver
of the space in the abdomen.
for processing. Fatty acids enter
lymph capillaries (green) for
their journey to the liver.

Direction of
blood flow

129

FUELING THE BODY

BUMPY SURFACE

The inside of your small intestine is
lined with thousands of tiny bumps
called villi. This magnified view
shows the fingerlike extensions on
the surface of a villus. These provide
a massive surface area to speed up
digestion and absorb nutrients.

FUELING THE BODY

End of the line

FUELING THE BODY The final section of the digestive tract, the large intestine,
is twice the width of the small intestine but only one
quarter of its length. The large intestine receives
watery, indigestible waste from your small
intestine. Here, it absorbs valuable water
from that waste, forming semisolid feces
(poo) that are pushed out of your body.

THE BOWELS OF THE BODY The ascending One of three The transverse
colon rises up bands of muscle colon passes across
The large intestine has three parts—the the right side of that run along the abdomen, just
cecum, the colon, and the rectum. The the abdomen. the length of below the stomach.
longest section, the colon, forms and moves the colon.
feces, which contain waste food, dead cells,
and bacteria. They eventually arrive in the
rectum and are expelled when you feel an
urge to go to the bathroom.

▶ COLON This Circular
cross-section shows the muscle layer
muscles that produce the
movements of the colon. A valve stops waste Feces inside
The lining releases from flowing back into the S-shaped
slippery mucus the small intestine. sigmoid colon.
to moisten feces
and make their
passage easier.

Band of The cecum is the The appendix
lengthwise first part of the sticks out from
muscle large intestine. the cecum.

Lining
of colon

LOOK CLOSER: FRIENDLY BACTERIA Rectum Anus

Your colon contains trillions of bacteria, The digestive process
many of which are friendly or helpful to also produces waste
the body. They digest material that human gases, which are
enzymes cannot, releasing useful nutrients, expelled through the
such as vitamin K, which the body absorbs. anus. Flatulence, or
“passing gas” as it
▶ COLON BACTERIA is known politely, can
The lining of the colon be noisy and smelly!
(brown) is covered by
bacteria (purple) that

feed on undigested food.

132

MOVING THINGS ALONG

As indigestible waste food is mixed and formed into that run the length of the colon. Movement of material
feces, it is propelled along the colon by three types of along the colon is slower than in other parts of the
movements (below). All are produced by contractions digestive system. This gives more time for as much
of the circular muscles and the three bands of muscle water as possible to be absorbed from the waste.

▲ SEGMENTATION Every ▲ PERISTALSIS Alternating ▲ MASS MOVEMENTS FUELING THE BODY
30 minutes, the muscles contract waves of muscular contraction Three times a day, powerful
to pinch waste into pellets that and relaxation push the pellets contractions force feces from the
are mixed but not moved. towards the rectum. descending colon into the rectum.

The descending colon WOW! WHY THE APPENDIX?
travels down the left
side of the abdomen. Always wash your The thin, dead-end tube called the
appendix was once thought to have
Pouches in the hands after going to the no function at all in humans. Scientists
colon are called now believe that it plays a part in our
haustra. bathroom. Feces are 50 body’s defenses, forming part of the
immune system. It also stores friendly
percent bacteria, and bacteria to replace those in the colon,
in case they’re flushed out during an
some are harmful. attack of diarrhea (runny feces).

Bladder Feces are pushed
downward by
contractions of
the rectum wall

Anal canal Anus ◀ WASTE DISPOSAL ▲ XRAY OF THE APPENDIX
links rectum Contractions of the colon push This colored X-ray image shows the
to anus feces into the normally empty slender, fingerlike appendix located
rectum. This stretches the rectum near to where the small intestine
wall, triggering an urge to go (right) joins the large intestine (left).
to the bathroom. Two powerful
sphincter muscles, which keep
the anus closed, relax. The
rectum wall contracts and
pushes the feces out through
the open anus.

Anal sphincter
muscles relax
to allow feces to
pass through

133

Chemical A branch of the hepatic The inferior vena cava
vein carries blood processed takes oxygen-poor blood
by liver cells to the inferior back to the heart.
vena cava (a major vein).

factory The hepatic portal vein
carries nutrient-rich blood
from the stomach
and intestines.

FUELING THE BODY The largest internal organ, the liver,
is your body’s chemical factory.
It performs almost 500 different
functions, including processing
the nutrients released from food.
It also makes the bile your digestive
system uses to help break down fats.

VITAL ORGAN

The liver is important because it processes, stores,
and makes so many substances. For example, it
stores and releases energy-rich glucose, processes fats
and amino acids, stores vitamins and minerals, breaks
down toxins and drugs, and recycles red blood cells.
It also releases heat, helping to keep you warm.

Central vein removes Surface The bile duct
processed blood of lobule collects bile from
the liver cells.
LIVER LOBULES Lobule
shown in
The liver contains around cross-section
one million sesame seed–sized
processing plants called
lobules. Inside a lobule, liver
cells are arranged in plates that
radiate out like spokes from
a central vein. The cells filter
substances out of the blood as
it flows towards the vein and
add other substances to it.

Branch of ▲ LIVER CELLS Also called
bile duct hepatocytes, these cells perform
hundreds of tasks, including
▶ LOBULE STRUCTURE Three Branch of Branch of hepatic storing glucose, making proteins,
vessels run along each corner of the hepatic artery portal vein carries and removing toxins (harmful
lobules. Two supply blood for supplies blood blood rich in nutrients substances) from the blood.
processing. The third, a bile duct, for processing
removes bile made by the liver cells.

134

The esophagus The hepatic artery LOOK CLOSER: BLOOD CLEANERS
carries food from carries oxygen-rich
the throat to the blood into the liver. The small blood vessels that pass between liver cells
stomach. are lined with macrophages (cells that eat other cells)
called Kupffer cells. They “clean” blood by removing
worn-out red blood cells, along with bacteria and debris.
The iron retrieved from red blood cells is recycled.

Left lobe of liver FUELING THE BODY

The stomach lies ▲ KUPFFER CELLS This incredible magnified
behind the liver. image shows a Kupffer cell (yellow) trapping and
consuming old red blood cells (red).
WOW!
Esophagus
The liver receives Stomach
2½ pints (1.5 liters)
Spleen
of blood every
minute. Hepatic
portal
Gall bladder vein

BLOOD SUPPLY Small
intestine
The liver has two blood supplies. The hepatic artery
delivers oxygen-rich blood from your heart. The hepatic 135
portal vein carries blood from your digestive organs and
supplies 80 percent of the liver’s blood. Nutrients and
other substances in the blood are processed by the liver.

Large intestine

▶ HEPATIC PORTAL VEIN
Veins from many parts of the digestive system,

including the stomach and intestines, join
together to form the hepatic portal vein, which

takes nutrient-rich blood to the liver.

Balanced diet COUNTING CALORIES

Eating the same kind of food every day wouldn’t only The amount of energy contained in different
be boring; it would be bad for your health. To stay foods is measured in calories. A cheeseburger,
healthy and at the right weight for your height you packed with energy-rich fat, contains many more
need to eat a balanced diet. This means eating sensible calories than, say, an apple. If you regularly eat
amounts of different foods from five main food groups. more calories than you need, the extra energy
will be stored by your body as fat and you will
become overweight.

FUELING THE BODY FIVE A DAY

You should try to eat at least five portions of
fresh fruits and vegetables every day. Scientists

have found that a diet including plenty of fruits
and vegetables can help reduce the chances of
developing serious diseases, such as cancer and
heart disease, later in life.

FOOD GROUPS Fruit Proteins

To stay healthy, you need to eat the
right foods in the right quantities, as
shown in the chart here. Eat a lot of
grains, such as wheat, since they
contain starch, which provides
fuel—in the form of glucose—to
your body. Vegetables and fruit
are rich in minerals and
vitamins. These help your
body cells work normally.
Dairy products contain
calcium, needed for
healthy bones and teeth.
Finally, protein-rich
foods provide the
building blocks for
growth and repair.

Grains

136

100 calories 360 calories 650 calories 200 calories 30 calories FUELING THE BODY

HOW MUCH ENERGY? Daily intake of calories Age 9–11 12–14 15–17 18+ WOW!
2280 2640 2880 2550
The amount of energy we need Polar explorers who pull
each day depends on a number 2050 2150 2150 1940 their own sledges need
of factors. Teenagers need more as much as 6,500 calories
energy than adults because they per day to survive in the
are still growing. Men need more cold, icy conditions.
calories than women because, on
average, they are bigger and have
more energy-burning muscle.

FAST OR SLOW?

Fast foods, such as burgers, contain large
amounts of fats and salt. They are
often eaten with soft drinks that
contain lots of sugar. It is
healthier to eat “slow” foods
prepared from a balanced
mix of fresh ingredients.

Dairy products Vegetables

137

FUELING THE BODY FOOD MARKET

This colorful food market in Malaysia
shows the wide variety of vegetables
eaten as part of the Southeast-Asian
diet. Eating lots of fresh fruits and
vegetables can help keep you healthy
and reduce your chances of developing
heart disease and cancer later in life.

FUELING THE BODY

FUELING THE BODY Vitamins WOW!

In addition to providing fuel for your body, Not all vitamins come
food contains the 13 vitamins that are vital from food. Vitamin D is
to health. You need only tiny amounts, but vital for bone growth. One
vitamins keep you looking good and feeling form of it is made by your
fine—going without them can damage skin when it is exposed
your health and cause nasty diseases.
to sunlight.

WHAT ARE VITAMINS? CHICKEN FEED

Each vitamin is a complex natural In the past, many people
chemical that has a special job in the in Southeast Asia died
body. Vitamins are known by a letter from a wasting disease
of the alphabet, and sometimes a called beriberi. In the 1890s,
number. Ascorbic acid, for example, is Dutch doctor Christiaan
usually called vitamin C, and riboflavin Eijkman found that chickens
is vitamin B2. You get vitamins from fed only white rice got the same
certain foods in your diet. disease, but those given brown rice
were healthy. The brown rice contained
Dairy products, vitamin B1, which prevented beriberi.
such as milk,
are full of Leafy greens, such Citrus fruits are
vitamin A. as cabbage and a good source of
spinach, contain vitamin C.
vitamin K.

Eggs are a Chicken and Wheat germ
good source other meats contains
of B vitamins. contain B vitamins. vitamin E.

140

SICK SCIENCE FUELING THE BODY

Eating food rich in vitamin B12 cures
a disease called pernicious anemia. In
1928, Dr. William Castle discovered
that a protein made by the stomach
helps the body absorb the vitamin. He
tested this by giving anemia patients
vitamin-rich food mixed with liquid
strained from his own vomit! Sure
enough, they got better more quickly.

NIGHT VISION

The ancient Romans had a strange cure for people who
couldn’t see at night. They roasted a goat and rubbed fat
from its liver onto the eyes of the patient, who also ate
some of the liver. But it worked! Why? Because liver is
rich in vitamin A, which helps you see in the dark.

DEADLY VITAMIN

Although vitamin A is vital to
health, you can have too much
of it. The livers of some animals
contain so much vitamin A that
they are dangerous to eat. The
Arctic Inuit people have long
known not to eat the livers of
polar bears, seals, or husky dogs.
However, several European
explorers, desperate for food on
long polar expeditions, found out
the hard way when they became
very ill after eating this meat.

FAST FACTS CRAZY CORN

■ The best way to make sure you get In the early 1900s, a strange disease swept
enough vitamins is to eat a wide variety of across the southern United States.
foods, and not stick to just a few favorites. Victims went mad and suffered sores
■ Vitamin C is a vital part of the human on their skin. In 1915, Dr. Joseph
diet, but most other animals are able Goldberger found that he could cause
to make their own. the symptoms by feeding people
■ Some common foods have vitamins nothing but corn—a staple of the local
added to make them more nutritious. diet—and cure them with a dose of yeast
■ Before they are born, babies need extract. He realized the disease was related
vitamins supplied by their mothers. to something missing from corn but found
in yeast, later identified as vitamin B3.

141

WASTE DISPOSAL WASTE
DISPOSAL

Every day your kidneys clean WASTE DISPOSAL
hundreds of pints of blood
and filter out harmful waste
chemicals. The wastes are
flushed out of your body in
urine, along with water your
body doesn’t need.

WASTE DISPOSAL Urinary Right kidney The renal
system artery carries
The inferior vena cava blood into
Your body’s cells release returns blood to the kidneys.
poisonous waste products. the heart.
Many are flushed out of the The renal
body by the urinary system. vein carries
Two kidneys process your blood out of
body’s blood and remove the kidneys.
excess water and waste. This Left kidney
waste liquid, called urine The aorta carries
(pee), is carried to the bladder, blood from
and released from the body the heart.
via the urethra when you go
to the bathroom. The left ureter
carries urine from
FILLING THE BLADDER the left kidney
to the bladder.
The kidneys produce urine. It is then pushed
The urethra carries
by waves of muscle contraction along the urine out of the body.

two ureters to the bladder. Urine

is stored in the bladder until the

bladder sends messages to the

brain indicating that it needs

to be emptied. Urine then

flows out of the body

along the urethra. Right ureter

▶ LONG AND SHORT The bladder stores
In the female system (shown urine and releases it
here), urine is expelled out when convenient.
of the body through a short
urethra. The male system is
the same except that the
urethra is longer and
passes along the penis.

144

DAILY BREAKS WOW! WASTE DISPOSAL

We make up to 2½ pints (1.5 liters) of urine every Your hardworking
day—enough to fill half a dozen coffee cups. When your kidneys make up just
bladder is full, nerve endings in the bladder’s muscle wall 1 percent of your weight,
signal to the brain that it is time for a bathroom break. A
sphincter muscle keeps your bladder shut until you are but they consume
ready to pee. The sphincter muscle relaxes and the 25 percent of your
bladder contracts to help push the urine out.
body’s oxygen.

OTHER JOBS

Your kidneys don’t just filter and clean blood to make urine.
They help control your blood pressure to make sure it stays
within safe limits. Your kidneys also release a hormone
(chemical messenger) that increases the production of red
blood cells in your bones. What’s more, they activate vitamin
D made by the action of sunlight on the skin. Active vitamin D
is needed in the body to make sure that bone-building calcium is
absorbed from the small intestine.

FAST FACTS KIDNEY MACHINE

■ Every minute of the day, about a quart Sometimes the kidneys stop
(liter) of blood passes through your working properly due to
kidneys to be filtered and cleaned. disease. One solution is to
■ It takes less than an hour to clean your transplant a healthy kidney
entire blood supply. into the body of a person with
■ Each kidney contains around one failing kidneys. But this isn’t
million tiny filtration and urine-making always possible. Kidney
units called nephrons. dialysis is an alternative
■ In an average lifetime, the kidneys treatment, which cleans a
process 12 million gallons (45 million patient's blood by passing it
liters) of blood, enough to fill 18 through a machine that acts
Olympic-size swimming pools. like an artificial kidney.

145

WASTE DISPOSAL

WASTE DISPOSAL

TESTING THE WATER

In the past, doctors used uroscopy—or
urine gazing—to help them diagnose
diseases, as shown in this 15th-century
woodcut. They would examine the
color, smell, and cloudiness of a
patient’s urine. Sometimes doctors
would also taste it!

WASTE DISPOSAL Waterworks

For your body to work at its best, the substances that
make up your blood have to be carefully controlled.
Your kidneys play a key role in this. All through the
day and night, they remove excess water, salts,
and poisonous wastes from your blood to make
urine. The cleaned blood is then returned
to your body’s blood supply.

INSIDE A KIDNEY The cortex is
the outer part
A network of blood vessels delivers blood to of the kidney.
and from the cortex (outer part) and the
medulla (inner part) of your bean-shaped The hollow
kidneys. These areas are where urine is renal pelvis
made. Urine then drains into the renal collects urine.
pelvis, a flattened, funnel-like tube, which
empties it into the ureters for the next
part of its journey out of the body.

The renal artery
delivers the blood that
has to be cleaned.

The renal vein
removes the
cleaned blood.

▲ BLOOD FILTERS The ureter The medulla is
A microscopic view of the kidney carries urine the inner part
reveals the tiny nephrons that away from of the kidney.
loop between the kidney’s cortex the kidney.
and medulla. They produce
urine by filtering blood.

148